1. Field of the Invention
The invention relates in general to a system and method of substrate handling in semiconductor processing, and specifically to a robot arm with primary and secondary substrate locations on a paddle-type end effector.
2. Description of the Related Art
In the processing of semiconductor devices, such as transistors, diodes, and integrated circuits, a plurality of such devices are fabricated simultaneously on a thin slice of semiconductor material, termed a substrate or wafer. Such wafers are extremely brittle, and easily contaminated. During manufacturing of semiconductor integrated circuits, therefore, care must be taken to avoid physical damage and particulate contamination to the wafers.
Various systems are known for handling wafers within semiconductor processing systems. The particular application or environment from which the wafer is lifted often determines the type of pickup device. One class of pickup devices, known as Bernoulli wands are typically used for high temperature applications. Bernoulli wands utilize jets of gas downward from the wand toward the wafer to create a region of low pressure above the wafer, therefore lifting it. The advantage being that the hot wafer need not contact the pickup wand, except perhaps at one or more small locators depending from the wand. Such a Bernoulli wand is shown in U.S. Pat. No. 5,080,549 to Goodwin, et al.
Another type of wafer pickup device is a simple paddle which relies on friction due to gravity between wafer support surfaces and the back of the wafer. In a variation of that, the paddle is augmented with a vacuum to hold the wafers on the paddles.
U.S. Pat. No. 5,135,349 to Lorenz, et al., discloses a robotic handling system utilizing two paddle style pickups mounted on a common rotating base. Both pickups are adapted to extend linearly away from one another to speed up handling of wafers within the processing system. Again, the paddles are augmented with a vacuum generated through a plurality of holes in an end effector portion of each paddle.
In a more recent method of wafer handling, a dual-arm transfer assembly is provided with one arm having a spatula-type end effector, and the other a Bernoulli wand end effector. This method uses the spatula to retrieve or deposit a wafer from or to a cassette. Prior to insertion into the process chamber for deposition, the wafer is “handed off” to the Bernoulli wand, which then places the wafer into the process chamber. Following processing, the Bernoulli wand retrieves the wafer from the process chamber and retracts it into the wafer handling chamber, where the wafer is deposited in a cooling station. When sufficiently cool, the spatula is used to return the wafer to the cassette in the load lock. This sequence of placing/retrieving a wafer from the cool station and returning it to it's cassette, fetching the next wafer and returning to the Bernoulli hand-off position is relatively short, but yet reducing the time is desirable. These robotic motions are typically conducted during the etch cycle where the process chamber is not available to process wafers. As improvements are made in process technology, the etch cycle may be significantly shortened or eliminated. Hence, there is a need for a system that reduces wafer handling time.